1. Field of the Invention
The present invention relates to a process for refining a zein, and more particularly a process for treating a solution containing crude zein with an acetone solution to remarkably decrease inherent smell and color thereof.
2. Related art
Zein is a main component of corn proteins and dissolves in various alcohols and alkali solutions. The zein solution shows adhesiveness and has an ability to form films and fibers. For instance, when the zein solution is applied by spraying, dipping or the like on the surface of an object and dried, a film is formed thereon, which has excellent water, acid and heat resistance. It also has excellent electric insulation ability. Therefore, zein has widely been employed as a raw material for preparing waterproof materials for papers, paint for wood works, adhesive for plywoods, damp-proofing agents, coating agents for foods and tablets (medicine), and the like.
Various processes have been proposed for extracting and refining the zein.
In Jap. Pat. No. Sho 61 (year of 1986) - 167700(A) and Martinue NiJhoff et al "Seed Proteins Biochemistry, Genetics, Nutritive Value", page 275-285 (1983), there are described extraction processes, wherein corn gluten meal or the like material containing the zein is treated with 70-90% (V/V) ethyl alcohol about 90% (V/V) isopropyl alcohol or the like water-containing lower alcohol solution, and distilling out the alcohol to obtain the zein. In Jap. Pat. No. Sho 50 (year of 1975) - 16800(B), there is described a process, wherein the zein is extracted from wheat gluten with 60-95% (V/V) aqueous acetone, methylethylketone or diethyleneglycol solution under stirring at temperature of 50.degree.-70.degree. C.
The zein obtained by the above conventional processes has an inherent smell and color and thus can not sufficiently satisfy recent severe requirements in food, medicine preparation and other industries. Further, it is difficult to supply a stable zein product with nice quality, because of the fluctuation in quality of the raw materials to be used, when such conventional processes are applied.
As processes for treating the zein, there are those, wherein the zein containing alcohol or alkali solution is cooled to cause a precipitation of the zein component and the resulting block-like precipitate is dried ["Industrial and Engineering Chemistry", Vol. 33, No.3, page 394 (1941)], and wherein the zein solution is poured into water or salt solution, for instance sodium chloride solution, to cause a precipitation of the zein and the resulting precipitate is dried to obtain the zein product which has good solubility in ethyl alcohol [Jap. Pat. No. Sho 63 (year of 1988) - 185999(A)].
The former process has disadvantages in that the block-like precipitate is difficult to wash. Further, the solution should be kept at a temperature of -20.degree. C. or below in order to avoid denaturation of the zein due to the water contained therein. The severe cooling condition and subsequent drying increase the cost. While, the latter refining process also has disadvantages in that the color and smell can not be removed sufficiently, cooling of the precipitate is required to avoid denaturation and freeze-drying of the precipitate results in an increase of a cost.
In view of such technical state of the arts, the present inventors have proposed in the specification of Japanese Patent Application No. Hei 3 (1991) - 117893 which substantially corresponds to United States application Ser. No. 07/868,907 a process for treating zein containing material to decrease at its smell and color, by combining the extraction of zein component with an alcohol, and more particularly ethyl alcohols and purification or washing of the zein component with acetone solution.
However, the zein treated by the last-mentioned process is not perfect with respect to the disappearance of its smell and color, and may cause some denaturing thereof during its drying step and holding period of time.